Self Assembly of Colloidal Polymers Using Isotropic Potentials

Self-assembly of spherical colloids into fluidic chains with no directional bonding or external perturbation promises to be a facile approach to engineer “designer” materials for enhanced surface transport, catalysis, optics, etc. Employing an Inverse Design technique (Relative Entropy optimization), we discern radially-symmetric pair potentials that result in the formation of fluidic, single-stranded, polydisperse colloidal strings (“colloidomers”). Comparing these potentials with those that form size-selective, compact, isotropic colloidal clusters, we find that the ranges of attraction (δ_A) and repulsion (δ_B) between the two are distinctly different. The energetics combined with the ranges determine the resulting structural motifs. A simple universal potential form is proposed whose morphological phase diagram predicts a gamut of microstructures as a function of δ_A and δ_B at fixed energetics and packing fraction. Four main broad classes of structures are observed - (i) dispersed monomeric fluid, (ii) ergodic, short chains as well as porous, space-spanning, one-monomer diameter thick, percolated strings, (iii) clusters and (iv) thick cylindrical structures including the tri-helical Bernal spirals.